The present invention relates to a pressure-controlled injector with force-balancing capacity.
In the modern injection systems for direct injection of internal combustion engines it is required that the injection pressure and the injection volume for which operational point of the engine can be determined independently from one another. In connection with this, an additional degree of freedom is created for the formation of mixture. In addition it is required that the injection volume at the beginning of the injection is as small as possible in order to take into account the ignition delay. These requirements are taken into consideration by injection systems with high pressure collecting chambers (common rail).
The patent document DE 198 35 494 A1 discloses a pump-nozzle unit. The unit serves for supplying the fuel into a combustion chamber of a direct-injection internal combustion engine. A pump unit is provided, with which an injection pressure is created. Fuel is injected via the injection nozzle into the combustion chamber. The pump-nozzle unit includes a control unit as well as a control portion. The control portion is formed as an outwardly opening A-valve, and by means of a valve operating unit is controllable for regulation of the pressure build-up in the pump unit. In order to create a pump-nozzle unit with a control unit which has a simple construction, is compact and has a short response time, the valve operating unit is formed as a piezoelectric actuator.
Patent document DE 37 28 817 C2 discloses a fuel injection pump for a combustion engine, which includes a pressure portion for pressurizing the fuel, a nozzle portion for injecting the pressurized fuel, and a control portion arranged between a pressure portion and the nozzle portion. The control portion intersects a fuel supply line that connects the pressure portion with the nozzle portion. Its end is formed as a control or regulating bore, which passes into an opening connected to the fuel return channel. In the channel, a control valve member is provided, which is movable by an electric operating unit between an opened position in which the fuel supply line and the fuel return channel are connected via the control bore and a closed position in which the control bore is closed.
The operating unit has a longitudinally adjustable piezoelectric element which is connected to a drive piston. Its free face is opposite to a substantially smaller face of a drive tappet, which is adjusted mechanically by the control valve member. The free face of the drive piston is separated from the smaller face of the tappet by a hollow chamber filled with incompressible fuel. In the drive tappet, a passageway is formed which connects the hollow chamber with the fuel return channel in which a check valve is disposed for closing the passage way when the pressure in the hollow chamber exceeds the pressure in the fuel return channel. The check valve opens the passageway when the pressure in the hollow chamber is smaller than the pressure in the fuel return channel.
In addition, it is known to provide additional throttle positions in the injection process in order to approximate an ideal triangular form for the injection process. In connection with this, however, the stroke is affected on the one hand, while on the other hand additional throttle positions on the injector must be provided.
Accordingly, it is an object of the present invention to provide a pressure-controlled injector which avoids the disadvantages of the prior art.
In accordance with the present invention an injector for injecting high pressure fuel into the combustion chamber of an internal combustion engine is designed so that a triangular pressure process can be realized without negatively affecting the pressure through a separate throttle position.
In keeping with these objects and with others which will become apparent hereinafter, one feature of present invention resides, briefly stated in an injector for an internal combustion engine, comprising an injector housing having a pressure releasable control chamber for a vertical stroke movement and an annular chamber; an injector body closeable by said annular chamber; an inlet connectable to a high pressure collecting chamber and connected to and emptying into said annular chamber; an injection nozzle having a nozzle inlet and a nozzle chamber, with said nozzle inlet opened or closed by a sealing surface, a hydraulic spring associated with said injector body and including a control element impinged with high pressure via a volume of said hydraulic spring and via said inlet.
In accordance with the present invention, a hydraulic spring is integrated in the injector housing of the injector so that an upper face of the injector body and a face of an adjacent control element represent limiting areas of the control volume of the hydraulic spring. High pressure from a high pressure collecting chamber (common rail) accumulates at the opposite side of the control element, as well as in a valve chamber surrounding the injector body. Depending on the cross sectional area of the control element, various prevailing pressures in the high pressure receiving chamber are taken into consideration, so that with large strokes of the injector body and the nozzle needles, a regulation of the high pressure takes place.
Through the design of the hydraulic spring with respect to the control volume, as well as the effective hydraulic diameter of the injector body, the rigidity as well as the spring force of the hydraulic spring can be affected. A piston is admitted between the pins on the surface of the injector body, which projects into the hydraulic spring and the control chamber that controls the electrical movement of the injector body. The piston turns its vertical movement upon a pressure chain of the associated control chamber to the injector body. The pin diameter and the effective piston diameter of the injector body, which is vertically displaceable in the housing of the injector significantly affect the rigidity and spring force of the hydraulic spring element.
The control element can be formed simply as a control piston, from the manufacturing technology prospective, and the hydraulic cross-section definitely affects the control behavior upon higher nozzle needle strokes in view of the prevailing pressure in the high pressure collecting chamber.
The novel features which are considered as characteristic for the present invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.